guessing the tenths across the 1 km squares. In one's own county one can afford to buy
all the local 1:25,000 maps, but outside one's own area this gets prohibitively expensive.
A solution for those living in Essex is to buy the Philip's Street Atlas Essex 2005. This
is readily available from garages and newsagents and has large scale maps printed
fractionally larger than 1:25,000 and has the National Grid lines at 500m intervals. Each
500m square is printed at 21mm wide, so 100m = 4.2mm on the map. I can supply you
with a transparent grid for overlaying 1:63,360, 1:50,000 or 1:25,000 O.S. maps if you
e-mail me, or, if you have a HP printer I can send you a file to print out on overhead
transparency film.
It might seem obvious that what we are trying to do with a grid reference is to locate as
precisely as possible the location of a plant on the earth's surface, so that if a dot map is
produced for that species, the dot is in the correct square, be it a 10km (hectad), tetrad,
monad or 100m square. Despite the modern day plethora of accurate maps and GPS
devices, some organisations seem hell-bent on wrecking this relationship. In the case of
named sites such as nature reserves for example, several organisations use a notional
grid ref. in the centre of the site, often to totally spurious 100m 'accuracy', or even
worse, the access point to the site. While this is fine for locating the nature reserve on a
map or with a GPS, it makes a complete nonsense of a plant database if this reference is
used to locate the find of a local or rare plant. While it obviously doesn't matter so much
for an insect or bird, as they will move around the site, it docs matter for a plant. The
situation becomes even more ridiculous for extended sites such as Epping Forest and
Hatfield Forest which both extend across several 10km squares.
Despite all these contrived problems with defining a grid reference, an even larger number
of discrepancies arise through human error. Most of us suffer from minor dyslexic
inconsistencies that result in us writing down a 6 when we mean a 9, or in writing a grid
reference down as TL674,231 when we actually mean TL671,234. This can occur if
following making a note of the north-south and east-west 1km grid line numbers, we
then use a piece of paper divided into tenths from the scale at the base of the map, or a
transparent-overlay grid, to get the 100m values, and succeed in reversing the position
of the two last values when we write them down. I have also frequently written down the
entire set of eastings and northings in reverse order. Investigation of documented grid
references nationally shows these errors to be quite a common human failing.
The generation gap has also initiated a confusing difference between grid reference
terminology and the way that grid references are written down. Prior to the time of the
Atlas of the British Flora, 1962 -the grid reference TL671,234, would have had to be
written down as the easterly and northerly coordinates 5671,2234, since 52 is the
numerical equivalent of TL and the computer would need to have the coordinates in
numerical order. Then, when cards were issued for recording on a 10km sq. basis, the
'52' was relegated to the first two positions in the gird reference with a back slash to
separate it from the other 6 digits. Either way, however 52/671,234 or TL671,234 would
essentially have been an '8-figure grid reference'. With advances in computer
Essex Field Club Newsletter No. 55, January 2008 11